This invention relates to an electronic thermostat having a controller for normally controlling the activation of a heating or cooling system. In particular, this invention relates to utilizing the controller to eliminate a short circuit condition when a short circuit is detected in the thermostat.
Heating, ventilation and air conditioning (HVAC) systems are commonly used in homes and commercial establishments to provide temperature controlled environments. Generally, a thermostat is used to manually set a desired temperature in an area heated or cooled by the HVAC system. The thermostat includes a controller which controls the activation of the HVAC system. Thus, if the temperature in the area being heated or cooled has deviated from the desired temperature set on the thermostat, the controller will send a signal which will turn on the HVAC system.
During the installation of an HVAC system, there are occasions when wires connected to the thermostat are incorrectly attached by a worker or are accidently crossed at some point. Thus, the thermostat must be designed to handle temporary problems produced by such situations in order to ensure safe and reliable performance. One problem which is commonly created by crossed or switched wires is a short circuit. The short circuit produces large current flow through the printed circuit traces of the thermostat and, if not accounted for, the short circuit could result in a fire or permanent damage to the thermostat.
In order to properly protect thermostats from short circuit conditions, it has been therefore known to expand the widths of the printed circuit traces in the thermostat that carry the potentially large current flow. These traces must be of sufficient width to at least carry the large current flow until a fuse associated with the printed circuit traces is blown. The above solution to handling short circuit conditions is becoming increasingly more difficult to implement as thermostats become smaller and more compact. In this regard, the necessity of maintaining the widened printed circuit traces as a safety precaution reduces the ability to create more compact thermostats even though the widened printed circuit traces are only needed during short circuit conditions. In addition, since this method of protecting against short circuits allows current to flow until a fuse is blown, there is an added cost associated with replacing the fuse each time a short circuit occurs.